Best to be seen. If you cannot walk after having this happen, I suggest being seen again. It is possible that you have a fracture that cannot be seen on a plain xray. It is not uncommon to find a fracture on an MRI that cannot be seen on plain xray. Hearing a crunch sound and not being able to walk are good clues of a possible fracture. I suggest elevation, rest, and crutches for now to prevent weight bearing.